1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a structure of a flip chip using an SOI (Silicon On Insulator) substrate and a method of manufacturing the same.
2. Description of the Background Art
FIGS. 25 through 28 are schematic views for explaining a soldering method using a flip chip. FIGS. 25 and 26 are top views and FIGS. 27 and 28 are sectional views. Referring to FIG. 25, a plurality of electrode pads 103 made of aluminum are formed on an upper surface of a flip chip 100 already undergone dicing. A silicon nitride film 104 is formed on a part of the upper surface of the flip chip 100 where the electrode pads 103 are not formed. Referring to FIG. 26, a bump 105 is formed on the electrode pads 103 of the flip chip 100. Referring to FIG. 27, the flip chip 100 on which the bump 105 is formed is turned upside-down, and thereafter, is mounted on a pattern formed on a wiring substrate 170 by soldering. Further, as shown in FIG. 28, there is a case where the flip chip 100 is mounted on the wiring substrate 170, and thereafter, is sealed with resin 171.
FIG. 29 is a sectional view showing a structure of a conventional flip chip using an SOI substrate. A layer 102 is formed on a silicon substrate 101. The layer 102 includes a BOX (Burried Oxide) layer and a silicon layer of the SOI substrate, a semiconductor element selectively formed on the silicon layer and an interlayer insulation film formed on the semiconductor element and the silicon layer. A plurality of electrode pads 103a to 103d are formed on the layer 102. The electrode pads 103a to 103c are electrically connected to the semiconductor element through a tungsten plug filling a contact hole formed in the interlayer insulation film and a wiring made of aluminum. The electrode pad 103d is electrically connected to the silicon substrate 101 through a conductive plug 173 made of polysilicon, tungsten or the like, which fills a contact hole 172 extending from an upper surface of the layer 102 to reach an upper surface of the silicon substrate 101. Further formed on the layer 102 is a silicon nitride film 104 patterned so as to expose the electrode pads 103a to 103d. Formed on the electrode pads 103a to 103d are bumps 105a to 105d made of solder, respectively. The bump 105d is provided for fixing a potential of the silicon substrate 101.
FIGS. 30 through 34 are sectional views showing manufacturing steps of the conventional flip chip shown in FIG. 29 in sequential order. Referring to FIG. 30, an SOI wafer is prepared first, and after carrying out usual processes of manufacturing a semiconductor, a structure is obtained in which the layer 102 is formed on the silicon substrate 101. Next, referring to FIG. 31, a photoresist 174 having a predetermined opening pattern is formed on the layer 102 by photolithography. Next, the layer 102 is subjected to anisotropic dry etching using the photoresist 174 as an etching mask so as to expose a part of the upper surface of the silicon substrate 101. Thereby formed is the contact hole 172 having its side surface defined by the layer 102 and its bottom surface defined by the upper surface of the silicon substrate 101. Such a step requires anisotropic dry etching with a very high aspect ratio.
Next, referring to FIG. 32, after removing the photoresist 174, a conductive film 175 made of a polysilicon film, a tungsten film or the like is formed on an entire surface by CVD method in a thickness that can fill the contact hole 172. Next, Referring to FIG. 33, the polysilicon film 175 is removed by CMP method until an upper surface of the layer 102 is exposed. Thereby, the contact hole 172 is filled with the polysilicon 173. Next, referring to FIG. 34, after forming an aluminum film on the layer 102, the aluminum film is patterned, thereby forming the electrode pads 103a to 103d at predetermined positions on the layer 102. The electrode pad 103d is in contact with the polysilicon 173.
Subsequently, after forming a silicon nitride film on the entire surface, the silicon nitride film is patterned, thereby forming the silicon nitride film 104. Next, after dicing the SOI wafer, the bumps 105a to 105d are formed on the electrode pads 103a to 103d, respectively, thereby obtaining the structure shown in FIG. 29.
In such a conventional flip chip, however, the electrode pad 103d is electrically connected to the silicon substrate 101 through the polysilicon 173 which fills the contact hole 172 formed in the layer 102. Accordingly, this requires the steps of: forming the contact hole 172 in the layer 102 by anisotropic dry etching with a very high aspect ratio (FIG. 31); forming the polysilicon film 175 on the entire surface (FIG. 32); and etching back the polysilicon film 175 by CMP method (FIG. 33), resulting in difficulties in the manufacturing steps.
A first aspect of the present invention is directed to a semiconductor device. The semiconductor device comprises: an SOI substrate including a semiconductor substrate, an insulation layer formed on a main surface of the semiconductor substrate and a semiconductor layer formed on the insulation layer; a semiconductor element selectively formed on the semiconductor layer; an interlayer insulation film formed on the semiconductor element and the semiconductor layer; a first electrode pad formed on a main surface of the interlayer insulation film, being electrically connected to the semiconductor element; a first bump formed on the first electrode pad; a hollow selectively formed extending from the main surface of the interlayer insulation film to reach the main surface of the semiconductor substrate; and a second bump formed on the semiconductor substrate which defines a bottom surface of the hollow.
According to a second aspect of the present invention, the semiconductor device of the first aspect further comprises a second electrode pad formed on the main surface of the semiconductor substrate which defines the bottom surface of the hollow, wherein the second bump is formed on the second electrode pad.
According to a third aspect of the present invention, the semiconductor device of the second aspect further comprises an impurity region formed in the main surface of the semiconductor substrate which defines the bottom surface of the hollow.
A fourth aspect of the present invention is directed to a method of manufacturing a semiconductor device. The method comprises the steps of: (a) preparing an SOI substrate including a semiconductor substrate, an insulation layer formed on a main surface of the semiconductor substrate and a semiconductor layer formed on the insulation layer; (b) selectively forming a semiconductor element on the semiconductor layer; (c) forming an interlayer insulation film on the semiconductor element and the semiconductor layer; (d) forming a first electrode pad on a main surface of the interlayer insulation film, the first electrode pad being electrically connected to the semiconductor element; (e) selectively forming a hollow which extends from the main surface of the interlayer insulation film to reach the main surface of the semiconductor substrate; and (f) forming a first bump on the first electrode pad and a second bump on the semiconductor substrate which defines a bottom surface of the hollow, respectively.
According to a fifth aspect of the present invention, the method of the fourth aspect further comprises the step of (g) forming a second electrode pad on the main surface of the semiconductor substrate which defines the bottom surface of the hollow, the step (g) being executed after the step (e) and before the step (f), wherein the second bump is formed on the second electrode pad in the step (f).
According to a sixth aspect of the present invention, in the method of the fifth aspect, the steps (d) and (g) are executed by the same process.
According to a seventh aspect of the present invention, the method of the fifth or sixth aspect further comprises the step of (h) forming an impurity region in the main surface of the semiconductor substrate which defines the bottom surface of the hollow, the step (h) being executed after the step (e) and before the step (g).
In the semiconductor device according to the first aspect of the present invention, the second bump for fixing a potential of the semiconductor substrate is formed on a part of the semiconductor substrate defining the bottom surface of the hollow. This allows simplification of manufacturing compared to a type of semiconductor device in which the second bump and the semiconductor substrate are brought into electric contact with each other through polysilicon which fills a contact hole reaching the semiconductor substrate.
In the semiconductor device according to the second aspect of the present invention, the second bump is formed on the second electrode pad, resulting in improved adhesion of the second bump compared to the case of forming the second bump directly on the semiconductor substrate.
In the semiconductor device according to the third aspect of the present invention, it is possible to reduce a resistance value of the semiconductor substrate at a position being in contact with the second electrode pad.
With the method according to the fourth aspect of the present invention, the second bump for fixing a potential of the semiconductor substrate is formed on a part of the semiconductor substrate defining the bottom surface of the hollow in the step (f). This allows manufacturing to be simplified compared to a method of manufacturing a semiconductor device comprising the steps of: forming a contact hole reaching the semiconductor substrate; forming a polysilicon film on the entire surface so as to fill the contact hole; etching back the polysilicon film; and forming the second bump on the polysilicon film filling the contact hole.
With the method according to the fifth aspect of the present invention, the second bump is formed on the second electrode pad, which results in improved adhesion of the second bump compared to the case of forming the second bump directly on the semiconductor substrate.
With the method according to the sixth aspect of the present invention, the second electrode pad can be formed on the main surface of the semiconductor substrate in the step (g) without adding a specific step of forming the same.
With the method according to the seventh aspect of the present invention, it is possible to reduce a resistance value of the semiconductor substrate at a position being in contact with the second electrode pad.
An object of the present invention is to provide a semiconductor device and a method of manufacturing the same, in which a bump for fixing a potential of a silicon substrate can be formed by simplified steps.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.